The proposal is a new steroid enzymology research project to establish a heretofore unrecognized pathway of 19-nor-Delta 4-androgen biosynthesis and to isolate and characterize the non-aromatizing androgen 19-desmolase and 19-hydroxylase in mammalian adrenal glands. Specific aims are 1) identification of the new enzyme system in the dog and human adrenal glands, 2) development of a rapid enzyme assay method, 3) solubilization, purification, and reconstitution of the 19-desmolase system, 4) formation of antibodies and immunochemical comparisons with aromatizing 19-desmolase (estrogen synthetase), and 5) elucidation of the mechanism of non-aromatizing androgen 19-desmolation. Nineteen-Nortestosterone has potent biological activities and the properties of the synthetase may have important implications in the understanding of adrenal physiology and regulation of the reproductive process. A specific antibody is useful for morphological identification of steroidogenesis and has potential values for diagnostic use. Elucidation of the reaction mechanism is also significant to biochemistry and pharmacology. It will give new insights into our understanding of steroid enzymology, cytochrome P-450 catalyzed drug oxidations and carcinogenesis, and toward designs of effective inhibitors for specific enzymatic processes. The methods involve synthesis of steroids with and without deuterium, tritium, carbon-14 and oxygen-18 labels at stereoselective and/or regiospecific positions, structural studies and isotope distribution analysis, incubations with various enzyme preparations, identification of metabolites, solubilization, purification, and reconstitution of the enzyme system, antibody production, and immunochemical characterization.